3 

No. III.] 


i H 7 3 


[SECOND SERIES. 


PRICE’S RETORT FURNACE 


FOR 


REHEATING AND PUDDLING. 




PRINTED FOR PRIVATE CIRCULATION. 

A. L. HOLLEY. 


New York, July, 1877. 





\ 


Copyright. 

A. L. HOLLEY^ 
1877. 









Price’s Retort Furnace. 


--- 

Nearly two years since I called the attention of my clients 
to this furnace, which I had seen at Woolwich Arsenal in 
187d, and which was made the subject of a strongly commen¬ 
datory paper before the Iron and Steel Institute by Mr. I. 
Lowthian Bell in 1875. 

The system is this: The waste gases are employed, 1st, to 

preheat the solid fuel which is to be burned on the grate; 2d, 

to distil the gases from it regularly, so as to perfect their 

combustion ; and, 3d, to preheat the air for combustion. 

Either bituminous or anthracite coal may be used. 

«/ 

During the last winter, my assistant Mr. Laureau and 
myself, repeatedly examined the working and repairs of the 
furnace at Woolwich Arsenal. We found— 

1st. That seven heating and puddling furnaces had been con¬ 
structed there, that ten ordinary furnaces were about to be 
altered to the Price system, and that the invention was 
making progress elsewhere. 

2d. That an important change had been made in the con¬ 
struction—carrying the w T aste gases to the retort in an over¬ 
head flue, as shown in the accompanying engraving, rather 
than underneath the furnace, and so adapting the system to 
existing furnaces by simply substituting the new fire-box and 
retort for the old fire-box. 

The advantages claimed for the furnace, and the reasons for 
them, may be briefly summed up as follows: 

1st. Its cheapness and convenient adaptation to existing 
works. 

2d. Its economy as a reheating furnace in waste or oxida¬ 
tion. This saving averages a little above 2 per cent, of iron 




4 


heated (piles of large bars), at Woolwich. There is also a 
greater yield of iron in puddling. 

3d. Its economy in fuel. This, in both puddling and heat¬ 
ing, averages over 40 per cent., as compared with the ordinary 
furnace. It, however, furnishes no heat to boilers. 

The reasons are: approximately perfect combustion, chiefly 
by means of the interception of any free air that may come 
through the grate, by a constant stream of gas; and a regular 
temperature due to charging red-hot fuel upon the grate. 

Before proceeding with a description of the Price furnace 
and its results, I would remark that, as far as I am aware, the 
Siemens gas-furnace is the most highly developed and the 
very best type in use. But however indispensable the re¬ 
generative gas-furnace may be for steel-melting and for some 
other uses, it is always costly, and in old works it sometimes 
requires a great change, if not a complete transformation of 
plant. It also requires a depth of some ten feet below the 
working level, and this is often impracticable on account of 
water. Tanks, either of metal or of masonry, to protect 
regenerators from water, are unsatisfactory. 

Description.— The Price furnace is partially a gas-furnace, 
and it embraces some of the features of the regenerative sys¬ 
tem, as the temperature of the air, as well as that of the gas¬ 
eous and fixed constituents of the coal, is raised by the waste 
heat before it enters the chimney. 

Fig. I. is a longitudinal section through centre of furnace. 

Fig. II. is a horizontal section. 

Fig. III. is a cross-section through heating-chamber. 

Fig. IV. is a horizontal section through air-chamber and 
lower part of retort-chamber. 

Fig. V. is a vertical section through retort and air-chamber. 

A is a combustion-chamber or fire-box, furnished with grate- 
bars in the ordinary way ; B a heating-chamber or hearth, 
separated from A by the usual bridge; C the neck leading 
into a flue, D, opening to the retort-chamber E. In the centre 
of this chamber is a circular fire-brick pillar, F, on which is 
placed a cast-iron cylindrical air-vessel, G, protected all around 
by fire-brick. 


On tliis air-vessel G is built the retort II, the lower part 
of which is made of brick, while the upper part is of cast iron. 
At the top of the retort, and above the closed end of the 
chamber, is placed a hopper, I, in the throat of which are 
fitted two doors, J, worked by a lever from the ground. This 
feeding apparatus may be of any other suitable construction. 
In the fire-brick portion of the retort are two passages, L L, 
the one leading to the combustion-chamber, and the other to 
the outside of the furnace for the insertion of stoking tools to 
force the fuel forward into the combustion-chamber. The 
entrance to the outer passage is closed by a tight door. 

Near the bottom of the chamber E, and in a line with the cen¬ 
tre of the air-vessel G, are pipes, M M, inserted in the walls of 
the chamber and passing all around it, as shown in Fig. IY. On 
the inner side of these pipes, and opening into the chamber E, 
are a number of holes, N N N, leading into the space around the 
pipes M M, which space affords room for expansion and for a free 
circulation of heat. These pipes are connected with the blast 
from a fan or from any suitable blower, at Q. The air passes 
into the chamber G, and is delivered through the outlet R in 
the ash-pit S directly under the grate. 

It will be seen from this description that the retort-furnace 
embraces some of the best features of the regenerative system, 
while it entirely dispenses with its complications of producers, 
regenerators, and reversing-valves. 

To Start the Furnace. —The bottom of the retort is filled 
with wood upon which two or three hopperfuls of coal are drop¬ 
ped ; a fire is kindled on the grate, and the retort is gradually 
filled up as the wood and coal ignite. By the time the fuel at 
the top descends to the bottom it becomes heated to redness— 
it is, in fact, coke, when bituminous coal is employed. A con¬ 
tinuous supply of fuel is then kept up; it is all fed from the 
top, through the hopper, without access of air. 

The Working of the Furnace. —The gases generated in the 
lower part of the retort and in the combustion-chamber pass 
over the bridge into the heating-chamber, up the neck C, 
through the flue 1), thence into the retort-chamber, filling 
the spaces around, giving up their heat to the retort II, the air- 


6 


vessel G, and the air-pipes M M ; the residue is then carried 
down and passes through the flue K to the stack ; but the 
heat that was stored up in the gases is carried back into the 
furnace by the heated air and fuel. 

A very important feature is that a continuous stream of 
gases, which must, of course, be regularly distilled in the re¬ 
tort, passes over the grate and takes up any unconsumed air 
that may get through the grate, thus preventing it from going 
over the bridge and oxidizing the metal. 

It is important to keep the retort well filled, so that the 
fuel will heat gradually, which aids it in giving up its gaseous 
constituents without sticking to the retort. The grate is kept 
well covered with a bed of brightly-burning coke about 6 
inches in thickness. Every ten or fifteen minutes, according to 
the requirements of the case, some hot coke from the retort is 
pushed upon the grate. This hot coke does not cool the fur¬ 
nace, but keeps up an even temperature, which is indispen¬ 
sable to heating with the highest economy; and the coke gives 
off no watery vapor to oxidize the metal. 

At intervals a crooked rod is run from the back stoking- 
door up into the retort, so as to stir up the coal and check any 
tendency to clogging. This precaution seems to be quite suf¬ 
ficient. In case of emergency, however, a bar can be run 
through the hopper down into the retort; but this is never 
needed if the retort is kept full. 

It is not necessary to light up every week, as, by filling up 
the retort and closing the ash-pit doors and the chimney-damp¬ 
er, the fire is kept alive from Saturday till Monday, so that it 
can be brought up to working heat in an hour and a half on 
Monday morning. The fire being once started, the operation 
goes on uninterruptedly for weeks and months, except when 
stopped for occasional repairs. 

The blast has about the same pressure as in the ordinary 
furnace ; it has slightly more friction to overcome in the pre¬ 
heating pipes. The quality of the flame can be regulated by 
means of the air-pipe damper, and a reducing or oxidizing 
flame obtained as circumstances demand. In short, there is 
O C V 1 ^ running a retort-furnace than an ordinary 


7 


one, and any furnace-man with fair intelligence can, in a few 
days, learn how to manage it. 

Kesults in Puddling. —The retort-furnace and the ordinary 
furnace have been working side by side at Woolwich Arsenal 
for more than three years, under the same management and 
with the same coal and iron; any comparison between the 
two should therefore be a fair one. 

The first results obtained, as given by Mr. I. Lowthian Bell 
in his paper read before the Iron and Steel Institute at the 
meeting in 1875, are as follows: 

price’s SINGLE PUDDLING-FURNACE—COLD AIR. 

Pig-iron delivered to furnace...188 tons * u 

Scrap-iron “ “ 31 “ - 2 Y 4 8 o 

219 “ ina 

Fettling used.. 49 tons 

Coal. 149 “ -&U 

Puddled bars received. 184 tons AW 

Scrap-balls received. 28 


(< 


-8&1. 

2240 


212 


(< 


1 ( 16 . 6 . 

2240 


Consumption per ton of puddled iron and scrap-balls. 

Pig-iron and scrap-iron. 1 ton o 

Fettling. 526 lbs. 

Coal. 1570 “ 

This single furnace worked 12% tons of pig per week. 

price’s DOUBLE PUDDLING-FURNACE—COLD AIR. 

Pig-iron delivered. 603 tons - 

Scrap-iron. 82 “ 

685 “ 

Fettling used. 70 tons ?fl<j lbs. 

Coal. . 350 “ 2 |$o “ 

Puddled bars received. 578 tons £$$$■ 

Scrap-balls “ . 75 “ 

653 “ 1677 lbs. 

Consumption per ton of puddled iron and scrap-balls. 

Pig and scrap iron. 1 ton ^ 4 a 0 

Fettling. 240 lbs. 

Coal. 1,200 “ 

This double furnace puddled 25 tons of iron per week. 




























8 


These trials were made in furnaces worked by the draught of 
the chimney alone, the air entering the fire-place at the tem¬ 
perature of the atmosphere. In the following experiment a 
fan was used, and the air was delivered under the grate heated 
to 300° F. The work done in a week was 26 y 2 tons, instead 
of 25 when using cold air. 


PRICE’S DOUBLE PUDDLING-FURNACE—nOT-BLAST. 

Pig-iron delivered to furnace.26 tons mg 

Scrap-iron “ . 3 “ 


Fettling used. 5 tons 2 £ A 5 o 

Coal... 13 “ 

Puddled bars received. 

Scrap-balls received. 


29 


< < 


24 “ 
3 “ 




2.JL6.8. 
2 2 4 0 


Consumption per ton of puddled iron and scrap-balls. 

Pig and scrap iron. 1 ton 119 lbs. 

Fettling. 425 “ 

Coal. 1057 “ 


The charges in this double furnace were about half a ton, 
but in later practice, by using Witham’s mechanical rabble, 
the charges were increased to ^ ton, and the amount of coal 
consumed was brought down as low as 812 lbs. per ton of 
puddled iron. 


ORDINARY PUDDLING-FURNACE. 

In all their past and current experience at Woolwich there 
has never been used less than 2,576 lbs. of coal per ton of 
iron in the ordinary single puddling-furnace, and never less 
than 2,016 lbs. in the double furnace. 

The iron puddled is largely old cannon-balls and shells, and 
the coal contains from 8 to 10 per cent, of ash. As the two 
systems of furnaces are continually employed on the same 


kind of work, the following comparative table may be taken as 
a fair average result: 



Iron, 

charge 

cwt. 

Coal, 

common 

furnace, 

cwt. 

Coal, 

Price 

furnace, 

cwt. 

Gain 
per cent. 

Single furnace... 

5 

23 ^ 

18 

13 * 

9 * 

iy 2 

42 * 

47 

Double “ ... 

10 

“ “ (Witham’s rabble). 

15 

15 

50 
























9 


The following tables are the results of experience in 1876: 
NO. 14.— price’s single puddling-furnace. 


No. of shifts worked, 378. Charges, ton. 

Weight of iron charged. 469 tons 1,008 lbs. 


“ “ “ yielded. 


“ 939 “ 

“ scrap-balls. 


“ 1,834 “ 

“ “ fettling. 


“ 716 “ 

“ coal consumed. 

. 361 

“ 520 “ 

Loss on yield. 


2.35 per cent. 


Consumption of coal per ton (including 

scrap-balls).1,540 lbs. 

Fettling per ton. 474 “ 

no. 3.— price’s double puddling-furnace. 


No. of shifts, 142. Charges, % ton. 


Weight of iron charged.511 tons 1288 lbs. 

“ “ “ yielded. 507 “ 1664 “ 

“ “ scrap-balls. 46 “ 2072 “ 

“ “ fettling. 131 “ 2094 “ 

“ “ coal consumed.217 “ 784 “ 

Loss in yield.0.75 per cent. 

Coal per ton (scrap-balls included). 877 lbs. 

Fettling per ton. 532 lbs. 


After five heats a charge of one-half ton of scrap-iron is used, 
and from 6 to 10 per cent, of it is wasted with a cutting flame 
for the purpose of raising the bottom. The fettling used is a 
rich tap-cinder, and in some cases the yield of iron is higher 
than the charge. 

All the figures given above are official, from the books of the 
Royal Gun Factories, and can therefore be relied on. 

At Mr. Witham’s works, Kirkstall Road, several retort-fur¬ 
naces have for some time been in use for puddling, and their 
performance seems in every way to confirm the experience at 
Woolwich. At the fall meeting of the Iron and Steel Insti¬ 
tute Mr. Witham, after having stated that the coal consump¬ 
tion at his works in the Price furnace was 932 lbs. to the ton 
of puddled bars, went on to say: “I do not know whether 
it will be out of place for me to state here that I have nothing 
but double furnaces at work, with charges of 15-cwt. heats, 
all worked by my machine (a mechanical rabble), and that my 
last year’s average was 1,705 lbs. of coals used per ton of 


















10 


puddled bars produced, including getting up of furnaces and 
broken turns for furnaces standing occasionally, so that the 
retort-furnace shows a saving of 773 lbs. to the ton of puddled 
bars produced, or, in my case, a saving of 46 per cent, of 
fuel.” Mr. Witham also said that the waste was 3.3 per 
cent, and the fettling 735 lbs., this fettling consisting of 
1/% ore and tap-cinder. Mr. Witham said, in private 
conversation in March, 1877, that his retort-furnaces had 
been running without any trouble since 1874, and that the 
economy in fuel had remained close on to 50 per cent., 
while repairs and maintenance were no higher than in the 
ordinary system. 

Conclusions on Puddling. —In a late paper before the 
London Association of Foremen Engineers , Mr. James 
Iionald concludes a discussion of the Price furnace with the 
following facts: The puddling of 1 ton of iron is done with 
about 7 cwts. of fuel against about 18 cwts. in the ordinary 
furnace. In the Price furnace but 20 y? cw T ts. of pig are 
requisite for a ton of puddled bars, while 21 y 2 cwts. of pig are 
required in the ordinary furnace. There is also a saving in 
fettling, and a great saving in repairs, viz., Is. per ton against 
3s. in the common furnace. 

Results in Heating and Welding Ikon. —The retort- 
furnace seems to have even greater advantages for these pur¬ 
poses than for puddling, and the results obtained at Woolwich 
show it to be as economical as any known heating furnace. 
The iron made at the Royal Gun Factories is an exceedingly 
strong and dry iron, and the best practice in the ordinary fur¬ 
nace has been 896 lbs. of coal to the ton of iron reheated. 
This figure may seem high, but it must be remembered that 
the iron treated here is totally different from that used for 
rails, which is usually weak and cindery, having been puddled 
at a low heat; it is, therefore, reheated with a correspond¬ 
ingly small amount of coal. The use of the Price furnace has 
reduced the average amount of coal to 448 lbs., and in some 
cases as low as 420 lbs., per ton of finished iron, with from 5 to 
6 per cent, waste by oxidation against 7 to 8 per cent, in the 
ordinary furnace. The piles welded weigh from half to three- 


11 


quarters of a ton. Here then, is a clear saving of half the 
fuel and of 2 per cent, waste. 

The retort-furnace has never been used in heating steel in¬ 
gots, but from its working in heating iron, an approximate 
idea of its qualities as a steel-heating furnace can be formed. 
Mr. William Price, Chief of the Forge Department at Wool¬ 
wich, said, in the discussion on Mr. I. L. Bell’s paper: “It 
was just at the point when iron was cindering that a steel 
ingot was at its climax of heat, but at this point half of the 
work was yet to be done in the iron and as much more fuel 
burned. In the gun factories they had carefully observed that 
in dealing with large masses, twelve tons of iron would take 
ten hours to heat. At the expiration of five hours, cindering 
would commence, but it would take five hours longer before 
its temperature was raised to a fit state for welding, while at 
least as much more fuel would be used in the second period 
as in the first. It was, therefore, misleading to compare the 
results of furnaces heating steel ingots and those heating iron, 
as he was thoroughly convinced only one-half the fuel was 
necessary, and that, where a ton of iron took 8 cwt. of coal to 
heat it, a ton of ingots should not take more than 4 cwt., and 
lie should be very much surprised if they were not heated in 
the retort-furnace for 2 cwt. of coal per ton.” 

Gas Analyses. —Some analyses of the gases, as they pass 
the neck of the furnace, were made at the Royal Laboratory of 
the Ordnance Department. 

The analysis of the heating-furnace escaping gases was found 
to be as follows : 


Carbonic acid. 15.9 vols , or 22.8 by weight. 

Oxygen. 2.2 “ 2.3 

Nitrogen. 81.9 “ 74.9 


100.00 100.00 

Mr. Ronald, in the paper mentioned, says: “This ex¬ 
hibits an all but perfect result; the whole of the fuel 
is consumed in a condition so as to exert its utmost energy 
and greatest heating capacity, and give to the furnace the 
highest possible results that fuel can accomplish. Perhaps no 







12 


better evidence of perfect combustion lias ever been taken 
during a process of manufacture.” 

The analysis of puddling-furnace gases during the operation 


was: 

» I 

Carbonic oxide. 13.07 vols., or 13.39 by weight. 

“ acid. 7.76 “ 12.49 

Hydrogen. 7.35 “ .53 

Nitrogen. 71.82 “ 73.59 


100.00 100.00 

It will be seen that this analysis shows an excess of carbonic 
oxide, which fact is adverse to the theory of perfect combustion. 
But it is well known that in puddling this carburized flame is 
necessary, so as not to w'aste too much when the fine particles 
of iron are just coming to nature on the top of the bath ; or, 
in the words of the puddlers, “ The iron must be covered with 
flame.” 

Maintenance.— The cost of repairs and maintenance seemed 
at first to be about the same as in the ordinary system. Mr. 
William Price stated in 1875 that at Woolwich an ordinary 
reheating furnace gave 900 tons of iron heated at the rate of 
6d. per ton for repairs ; a reheating retort-furnace gave 1,000 
tons of iron heated at 6*4d. per ton ; an ordinary single pud¬ 
dling-furnace gave 470 tons of iron at a cost of 2s. lid., and a 
single retort-furnace gave 503 tons at a cost of 3s. ; a double 
retort-furnace gave 500 tons of iron at a cost of Is. 6d. per 
ton for repairs. Mr. Ronald, in the paper previously quoted, 
says the repairs of the double retort furnace have been reduced 
to Is. per ton. 

It would appear also from still more recent experience that 
this class of expenses has been reduced. Taking, for 
instance, the results of Ro. 3 Price furnace (before mentioned), 
obtained from December 10, 1876, to March 16, 1877, we find 
the corresponding expenses of repairs to have been as follows : 


Dec. 23.—Enlarging heating-chamber.. $12 50 

Feb. 10.—New bridge and sides to furnace, and repairing crown 

and jambs to dandy. 35 00 

“ 17.—New bottom and jambs to dandy. 14 00 

March 10.—New doors and repairing jambs and end of dandy. 12 50 


$74 00 













13 


During this period 551 tons 1,496 lbs. of iron were pro¬ 
duced, so that the repairs would amount to about 13^ cents 
per ton. In this double furnace, as will be seen by the items 
of cost, the neck of the furnace has been enlarged so as to 
make room for a “dandy,” or chamber next the throat of the 
furnace for preheating the iron. 

There is not included in the above the occasional cost of re¬ 
newing the cast-iron part of the retort, which generally lasts 
from 40 to 42 weeks, after which the lower section of it must 
be renewed. This is done by tearing down one side of the brick 
casing, or retort-chamber ; the retort is then taken out sidewise. 
This change is made in l J / 2 days. The retort sometimes 
cracks before it is quite worn out; in this case the cracked side 
is covered with bricks on edge, and this precaution is found 
sufficient to prevent any further damage. The air-apparatus— 
that is to say, the air-vessel G and the circuit pipes—lasts inde¬ 
finitely. The brick casing around the retort generally lasts as 
long as two cast-iron retorts. 

The repairs are much less frequent on heating-furnaces; they 
have sometimes run 26 weeks, welding large, dry piles, with¬ 
out any repairs except a new fire-bridge wall. 

Raising Steam vs. Regeneration. —Raising steam by the 
waste gases of heating and puddling furnaces has been deemed 
an important economy, especially in iron-mills where the fur¬ 
nace temperatures were high. But even in these cases, a 
comparison of the fuel burned economically in producers for 
regenerative furnaces, and under well-arranged boilers, with that 
burned necessarily w r astefullv in common furnaces with boilers 
over them, has shown a considerable economy in favor of ap¬ 
plying waste heat to regeneration. Although such a compa¬ 
rison has not been direct!}' made in the case of the Price fur¬ 
nace, a similar result may be predicated on the numerous trials 
with the Siemens furnace. 

The use of boilers over ste^-heating furnaces has not proved 
a success. In several prominent works, such boilers have 
been removed; they did not make steam enough to pay for 
attendance. 

9 

■ But the whole matter of the comparative saving of fuel by 


14 


regeneration and by steam-raising is of minor importance when 
compared with that of saving in the oxidation of the costly 
materials which are treated in the furnace. A saving of two 
per cent, in the oxidation of fine merchant iron in its average 
number of re-heats, could hardly be less than $1 50 per ton, and 
this would pay for a new set of furnaces in less than a year. 

It has, however, been proposed to raise steam by the waste 
heat of the Price furnace; for, well as it has utilized this heat, as 
proved by the foregoing results, there is still some left. Experi¬ 
ments made by the Woolwich authorities, extending over a 
period of two days, showed that the temperature in a reheat¬ 
ing-furnace stack varied between 1,100 and 1,400 degrees, the 
average being 1,260 degrees F. That in the flues of the pud¬ 
dling-furnaces ran higher, but the heat has never been accu¬ 
rately measured ; it is thought it would range between 1,600 
and 1,800 degrees; but it is questionable whether heat enough 
would be regularly obtained for the purpose of raising steam 
economically. The heat in the puddling-furnace is visibly much 
higher than in the heating-furnace ; for at five feet above the 
ground, the heating-furnace stack remains a dull red, while at 
the same height the puddling-furnace stack is often cherry- 
red. Loose bricks are left purposely in each stack, so as to ob¬ 
serve the heat; the furnace-man is thus enabled to judge of 
the temperature in his furnace, and can control it accordingly 
by the blast or by the amount of coal on the grate, as the case 
may be. 

Cost.— The furnace shown in the engraving (of which I 
have detail drawings) was designed to heat five or six 4-rail 
steel ingots or a larger number of double-rail blooms, but it 
is adapted to iron piles. It is 12 feet long on the bed. 

The important elements of cost are the following: 


Materials . 

Rubble. 

Common fire-brick, laid. 

Best “ “ ... 

Citings 011 1 not deluding hopper 

Bolts. 

Bar-iron. 


Quantities . 

. 57 feet. 
12K M. 

7 

j 5,000 lbs. 
t 41,000 “ 
1,350 “ 
2,000 “ 








15 


As the prices of these materials vary in different localities, 
I will not attempt to give an exact estimate. In round num¬ 
bers, this furnace would cost $3,000, not including the stack. 
Of this sum the hopper would cost about $200. 

The cost of altering an old furnace to the Price system 
would depend upon the situation of the furnace with reference 
to the stack, and upon other circumstances. Should the stack 
stand at the throat end, an underground flue could be readily 
brought to it from the retort-chamber; should the stack be at 
the retort end, the connection would be short and simple. 
An old furnace would require a new fire-box and a retort- 
chamber and its appurtenances. The plates of the old fire¬ 
box might be utilized. Probably altering an old furnace 
would cost $2,000. 

Mr. Ponald, before quoted, says that a double retort 
puddling-furnace, with Witham’s rabble, would cost, in Eng¬ 
land, only about $2,500. 

Conclusion.— I. While there can hardly be such perfect 
combustion and such control of the flame in this furnace as in 
a furnace where the fuel is exclusively gas, it is nevertheless 
obvious that the Price furnace has the economical advantage 
of utilizing the original heat of the gases—there is no heat 
wasted in producers and cooling tubes. 

II. The Price system will recommend itself very strongly 
for existing works, on account of its cheapness and its ready 
application to existing furnaces, or at least to existing mills, 
especially where it is impracticable, on account of water, to put 
regenerators ten feet below the mill floor. 

III. As the gases are uniformly distilled in the retort, their 
combustion, as they meet the air coming through the grate, 
must be approximately complete. 

IV. This constant flow of gases intercepts the air that comes 
through the grate and applies it to the combustion of fuel 
rather than to the combustion of iron. In the ordinary fire¬ 
box, a caking coal, especially, must make a fire of irregular 
thickness and often full of holes, so that much air passes over 
the bridge to oxidize the metal. 

V. Red-hot coke or coal, distributed regularly over the 


16 


grate, without the admission of air through the fire-door, tends 
to the maintenance of an even heat in the furnace; but firing 
cold fuel, which is also often wet, suddenly cools the furnace, 
fills the heating-chamber with smoke and watery vapor, and 
checks not only combustion but metallurgical operations. 

VI. The further utilization of waste heat and improvement 
of combustion by means of preheating the blast, has been tried 
in various ways with success. Price’s system seems to be 
thorough, and the apparatus is durable. 

Finally, it may be said that this furnace is now completely 
beyond the experimental stage, and that its construction and 
practice are settled and well defined. 


